The long range goal is to understand the biosynthesis and regulation of creatine production. Creatine plays an essential role in energy metabolism, serving as the major store of high energy phosphate in muscle and other tissues. The first step in creatine biosynthesis involves the enzyme L-arginine: glycine amidinotransferase, known as transamidinase. The regulation of this enzyme is the major site in control in creatine biosynthesis. Transamidinase is known to be controlled by the end-product of the reaction pathway, although the mechanism by which this occurs is not known. Towards this end, a cDNA clone homologous to rat kidney transamidinase mRNA will be isolated with the lambda gtll expression system and specific antibodies to transamidinase. This cDNA clone will be used to measure transamidinase mRNA levels and the rate of transamidinase gene transcription in the presence of creatine. Evidence to date indicates that transamidinase is made as a higher molecular weight precursor which is processed before it is transported. With the cDNA it will be possible to prove this by specifically analyzing the sequence of the mNRA and comparing it to the known sequence of the protein. Finally, the cDNA will allow us to investigate whether transamidinase is truely found in the liver, the site of subsequent reactions in creatine biosynthesis. Knowledge of the mechanisms of regulation and biosynthesis of transamidinase is crucial to the understanding and ultimately, maintaining the correct functioning of this important biological system.